This invention relates to a chromotographic process for purifying sugars and lignosulfonates from sulfite spent liquor.
Sulphite spent liquors are produced as a waste product from the production of wood pulp via the sulfite process. These liquors contain undissolved wood solids, lignins, and hexose and pentose sugars, as well as chemicals introduced in the pulping process. In the past, these waste liquors were frequently discharged into streams. Environmental legislation has put a stop to this practice, however, and some alternative disposal techniques and uses for sulfite spent liquor have been developed.
A significant portion of the sulfite spent liquor produced in pulp making is evaporated and burned, primarily as a source of heat. This practice faces its own environmental difficulties, however, due to the high sulfur content of the sulfite spent liquor. Effective utilization will require the fractionation of the sulfite spent liquor into its components parts.
Hassi et al. have disclosed a single-step chromatographic separation for separating sugars and lignosulfonates from sulfite spent liquor. H. Hassi, P. Tikka and E. Sjostrom, The Ekman-Days 1981, Stockholm 1981, Preprints Vol. 5, p. 65; 1982 International Sulfite Pulping Conference, TAPPI Proceedings, p. 165. The process utilizes a strongly acidic polystyrene cation exchange resin crosslinked with divinylbenzene to isolate four fractions. Two lignosulfonate fractions, one of which is essentially free of sugars, are isolated, along with a predominantly sugar fraction which contains moderately low levels of lignosulfonates. The fourth fraction contains lignosulfonates and sugars in roughly equal amounts.
Because of the fourth fraction, which amounts to about 30% of the dry-solids content, the process of Hassi et al. does not result in good yields of purified materials from sulfite spent liquor. Moreover, the sugar fraction isolated still contained over 7% lignosulfonates, and the level of impurity would be expected to get worse as larger, commercial size columns were used. Thus, this separation technique does not provide an effective industrial method for separating sulfite spent liquors into essentially pure components with a high yield.
It is the object of this invention to provide a method for separating sulfite spent liquor into essentially pure sugar and lignosulfonate fractions.
It is a further object of this invention to achieve this separation at high yield, and on a scale suitable for industrial application.